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LibSoftGPU: Dispatch based on ClipPlane enum at compile-time

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The `ClipPlane` enum is being looped over at run-time performing
run-time dispatch to determine the comparison operation in
`point_within_clip_plane`.

Change this `for` loop to be linear code which dispatches using a
template parameter. This allows for the `point_within_clip_plane`
function to do compile-time dispatch.

Note: This linear code can become a compile-time loop when static
reflection lands in C++2[y|z] allowing looping over the reflected
`enum class`.
This commit is contained in:
Lenny Maiorani 2022-01-27 17:18:07 -07:00 • committed by Linus Groh
parent 3c11dc5bd3
commit 2e436129b0
2 changed files with 40 additions and 33 deletions
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70
Userland/Libraries/LibSoftGPU/Clipper.cpp
View file

@ -1,54 +1,57 @@
/* /*
* Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com> * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
* Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org> * Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
* Copyright (c) 2022, the SerenityOS developers.
* *
* SPDX-License-Identifier: BSD-2-Clause * SPDX-License-Identifier: BSD-2-Clause
*/ */
#include <AK/Format.h> #include <AK/Vector.h>
#include <AK/ScopeGuard.h> #include <LibGfx/Vector4.h>
#include <LibSoftGPU/Clipper.h> #include <LibSoftGPU/Clipper.h>
#include <LibSoftGPU/Vertex.h>
namespace SoftGPU { namespace SoftGPU {
static constexpr FloatVector4 clip_plane_normals[] = { template<Clipper::ClipPlane plane>
{ 1, 0, 0, 0 }, // Left Plane static constexpr bool point_within_clip_plane(FloatVector4 const& vertex)
{ -1, 0, 0, 0 }, // Right Plane
{ 0, -1, 0, 0 }, // Top Plane
{ 0, 1, 0, 0 }, // Bottom plane
{ 0, 0, 1, 0 }, // Near Plane
{ 0, 0, -1, 0 } // Far Plane
};
static constexpr bool point_within_clip_plane(FloatVector4 const& vertex, Clipper::ClipPlane plane)
{ {
switch (plane) { if constexpr (plane == Clipper::ClipPlane::LEFT) {
case Clipper::ClipPlane::LEFT:
return vertex.x() >= -vertex.w(); return vertex.x() >= -vertex.w();
case Clipper::ClipPlane::RIGHT: } else if constexpr (plane == Clipper::ClipPlane::RIGHT) {
return vertex.x() <= vertex.w(); return vertex.x() <= vertex.w();
case Clipper::ClipPlane::TOP: } else if constexpr (plane == Clipper::ClipPlane::TOP) {
return vertex.y() <= vertex.w(); return vertex.y() <= vertex.w();
case Clipper::ClipPlane::BOTTOM: } else if constexpr (plane == Clipper::ClipPlane::BOTTOM) {
return vertex.y() >= -vertex.w(); return vertex.y() >= -vertex.w();
case Clipper::ClipPlane::NEAR: } else if constexpr (plane == Clipper::ClipPlane::NEAR) {
return vertex.z() >= -vertex.w(); return vertex.z() >= -vertex.w();
case Clipper::ClipPlane::FAR: } else if constexpr (plane == Clipper::ClipPlane::FAR) {
return vertex.z() <= vertex.w(); return vertex.z() <= vertex.w();
} }
return false; return false;
} }
static Vertex clip_intersection_point(Vertex const& p1, Vertex const& p2, Clipper::ClipPlane plane) template<Clipper::ClipPlane plane>
static constexpr Vertex clip_intersection_point(Vertex const& p1, Vertex const& p2)
{ {
constexpr FloatVector4 clip_plane_normals[] = {
{ 1, 0, 0, 0 }, // Left Plane
{ -1, 0, 0, 0 }, // Right Plane
{ 0, -1, 0, 0 }, // Top Plane
{ 0, 1, 0, 0 }, // Bottom plane
{ 0, 0, 1, 0 }, // Near Plane
{ 0, 0, -1, 0 } // Far Plane
};
constexpr auto clip_plane_normal = clip_plane_normals[to_underlying(plane)];
// See https://www.microsoft.com/en-us/research/wp-content/uploads/1978/01/p245-blinn.pdf // See https://www.microsoft.com/en-us/research/wp-content/uploads/1978/01/p245-blinn.pdf
// "Clipping Using Homogeneous Coordinates" Blinn/Newell, 1978 // "Clipping Using Homogeneous Coordinates" Blinn/Newell, 1978
float const w1 = p1.clip_coordinates.w(); float const w1 = p1.clip_coordinates.w();
float const w2 = p2.clip_coordinates.w(); float const w2 = p2.clip_coordinates.w();
float const x1 = clip_plane_normals[to_underlying(plane)].dot(p1.clip_coordinates); float const x1 = clip_plane_normal.dot(p1.clip_coordinates);
float const x2 = clip_plane_normals[to_underlying(plane)].dot(p2.clip_coordinates); float const x2 = clip_plane_normal.dot(p2.clip_coordinates);
float const a = (w1 + x1) / ((w1 + x1) - (w2 + x2)); float const a = (w1 + x1) / ((w1 + x1) - (w2 + x2));
Vertex out; Vertex out;
@ -62,21 +65,21 @@ static Vertex clip_intersection_point(Vertex const& p1, Vertex const& p2, Clippe
return out; return out;
} }
static void clip_plane(Vector<Vertex>& read_list, Vector<Vertex>& write_list, Clipper::ClipPlane plane) template<Clipper::ClipPlane plane>
FLATTEN static constexpr void clip_plane(Vector<Vertex>& read_list, Vector<Vertex>& write_list)
{ {
auto read_from = &read_list; auto read_from = &read_list;
auto write_to = &write_list; auto write_to = &write_list;
write_to->clear_with_capacity(); write_to->clear_with_capacity();
// FIXME C++23. Static reflection will provide looping over all enum values.
for (size_t i = 0; i < read_from->size(); i++) { for (size_t i = 0; i < read_from->size(); i++) {
auto const& curr_vec = read_from->at((i + 1) % read_from->size()); auto const& curr_vec = read_from->at((i + 1) % read_from->size());
auto const& prev_vec = read_from->at(i); auto const& prev_vec = read_from->at(i);
bool const is_curr_point_within_clip_plane = point_within_clip_plane(curr_vec.clip_coordinates, plane); bool const is_curr_point_within_clip_plane = point_within_clip_plane<plane>(curr_vec.clip_coordinates);
bool const is_prev_point_within_clip_plane = point_within_clip_plane(prev_vec.clip_coordinates, plane); bool const is_prev_point_within_clip_plane = point_within_clip_plane<plane>(prev_vec.clip_coordinates);
if (is_curr_point_within_clip_plane != is_prev_point_within_clip_plane) { if (is_curr_point_within_clip_plane != is_prev_point_within_clip_plane) {
auto const intersect = clip_intersection_point(prev_vec, curr_vec, plane); auto const intersect = clip_intersection_point<plane>(prev_vec, curr_vec);
write_to->append(intersect); write_to->append(intersect);
} }
@ -91,10 +94,15 @@ void Clipper::clip_triangle_against_frustum(Vector<Vertex>& input_verts)
list_a = input_verts; list_a = input_verts;
list_b.clear_with_capacity(); list_b.clear_with_capacity();
for (size_t plane = 0; plane < NUMBER_OF_CLIPPING_PLANES; plane++) { // FIXME C++23. Static reflection will provide looping over all enum values.
clip_plane(list_a, list_b, static_cast<ClipPlane>(plane)); clip_plane<ClipPlane::LEFT>(list_a, list_b);
} clip_plane<ClipPlane::RIGHT>(list_a, list_b);
clip_plane<ClipPlane::TOP>(list_a, list_b);
clip_plane<ClipPlane::BOTTOM>(list_a, list_b);
clip_plane<ClipPlane::NEAR>(list_a, list_b);
clip_plane<ClipPlane::FAR>(list_a, list_b);
input_verts = list_a; input_verts = list_a;
} }
} }

3
Userland/Libraries/LibSoftGPU/Clipper.h
View file

@ -1,5 +1,6 @@
/* /*
* Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com> * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
* Copyright (c) 2022, the SerenityOS developers.
* *
* SPDX-License-Identifier: BSD-2-Clause * SPDX-License-Identifier: BSD-2-Clause
*/ */
@ -13,8 +14,6 @@
namespace SoftGPU { namespace SoftGPU {
class Clipper final { class Clipper final {
static constexpr u8 NUMBER_OF_CLIPPING_PLANES = 6;
public: public:
enum class ClipPlane : u8 { enum class ClipPlane : u8 {
LEFT = 0, LEFT = 0,